Phenolic reaction products, identification

Lin, L. Z., Yao, Y. G., and Shiraishi, N. (2001) Liquefaction mechanism of beta-O hgnin model compound in the presence of phenol under acid catalysis. Part 1. Identification of the reaction products. Holrforschung 55(6), 617-624. 

It is interesting to compare early experimental work with the facilities available in a modem laboratory. Von Auwers was the first to separate the chloro ketones from the normal phenolic aldehydes of the Reimer-Tiemann reaction.21 Identification and structure proof by chemical means followed. It is a tribute to von Auwers skill and insight that his identification procedures have withstood the onslaught of modem spectroscopic means. Although the chloro ketones (equations 8-10) have been called the abnormal products of the reaction, in cases where the ortho and para positions are occupied (see equation 10) only ketonic material is obtained.1 22 In fact, the presence of the dichloro ketones provides one of the better arguments for the intermediacy of dichlorocarbene in the reaction mechanism.23... 

The identification of GDPPH-1 and GDPPH-2 as reaction products provided the first unambiguous evidence that the principal oxidation sites of garcinol are the 1,3-diketone and the phenolic ring part. 

In none of these studies was a reaction product actually isolated. The authors confined their work mainly to the hydrolysis of the conjugates with i8-glucuronidase and identification of the steroid residues. Consequently, it is still uncertain which glucosiduronates are formed in these experiments, and whether conjugation of the alcoholic or phenolic hydroxyl group is favored. 

The reaction products, unless solid crystalline compounds, are identified by procedures given in the discussion of the identification of alkyl halogenides (p. 136) and phenol ethers (p. 201). 

At present the only colored product that has been identified in the reaction of syringyl alcohol with aqueous alkali is 2,6-dimethoxyquinone. No evidence exists that dimeric chromophoric structures such as a dipheno-quinone or a stilbenequinone, which have been found to be products in the oxidative reactions of phenols in other studies (/, J, I5y 23), are also products of this reaction. However, with the identification of 2,6-dimethoxyquinone and the two colorless products, bis-4-hydroxy-3,5-dimethoxyphenylmethane and syringaldehyde, one of the logical pathways for the reaction is suggested and discussed. 

In this section, the phenol-formaldehyde reactive system is considered as an example of identification of reduced kinetic models. The kinetic model containing 13 components and 89 reactions, developed in Sect. 2.4 to study the production of 1,3,5-methylolphenol, is too detailed and complex for control and monitoring purposes. Thus, in this section this model is referred to as detailed model, while four reduced kinetic models, based on lumped components and reactions, are developed. 

A simple identification test is ordinarily required for parenteral pharmaceuticals. The identification test is typically a color development test performed by mixing the test product with a chemical reagent to produce a characteristic color. For example, phenolic compounds react with ferric chloride to produce an intense dark color. Sometimes when there is no unique color reaction test... 

Identification of Aromatic Amines.—Most aromatic amines are soluble in hydrochloric acid, and are precipitated from the solution of their salts so formed by bases. Aqueous solutions of the amines, even when very dilute, yield precipitates of bromine substitution-products when treated with bromine water. The reaction is not characteristic, however, as phenols act in a similar way. 

Identification of Phenols.—The reactions of phenols which are of particular value in their identification, are those that take place with alkalies, ferric chloride, and bromine water. Most phenols react with an aqueous solution of sodium hydroxide to form soluble salts, but are insoluble in a solution of sodium carbonate. The behavior of phenols with these two reagents shows their weakly acidic properties, and serves to distinguish them from acids. Phenols which contain strongly negative substituents decompose carbonates, and show all the properties of acids. It is difficult, therefore, to identify as a phenol substances which contain such substituents. Ferric chloride produces marked colorations in aqueous solutions of most phenols. The reagent produces a similar effect with certain other compounds, and the formation of a color with ferric chloride can be taken, therefore, only as an indication of the presence of a phenol. With bromine water most phenols yield a precipitate of a brominated phenol. Other compounds, amines for example, are also converted into insoluble substitution-products by bromine water. Notwithstanding this fact the test is of value. Many phenols form colored products when heated with phthalic anhydride and concentrated sulphuric acid. The reaction will be described under phenolphthalein (558, 639). 

---